Polycarbonate vs PET

If you read articles from manufacturers of polycarbonate and PET, the claims made for applications in bottle-making seem at odds. Data are produced to prove that PET or polycarbonate (depending on the origin of the article) is far superior for the production of 19 litre bottles. I have distilled information from several sources to try and provide a balanced picture.

In early history, water was stored in animal skins and large clay pots.  Although storage was temporary and the water was not always pure and sanitary, the containers served a need.  In more modern times water was bottled in glass containers, which were sanitary as well as clear, allowing consumers to see the contents.  However, they were also heavy and breakable.  As in all evolutionary trends, the industry began to look for a packaging material that would perform better than glass.

The search led to polycarbonate. Bottles made from polycarbonate were more durable than glass yet lighter.  Performance outweighed cost, hence the industry invested in new equipment and made the switch to polycarbonate.  Further searches for less expensive materials led to the use of PET, which transformed the convenience single-trip water market.  However, what about 19 litre, multiple-trip containers?

An important aspect is that the moulding techniques are completely different. This allows polycarbonate to have greater design flexibility such as integral moulded handles. PET bottles need a separately moulded solid handle (as shown).

However, PET has a better finish with smooth internal neck and no die lines or need for trimming. On the other hand, PET has a tendency to shrink at high wash temperatures which can cause leakage problems eventually.  PET is more flexible than polycarbonate and can often stand more impact punishment. The plastic distribution is better in PET bottles and the stress tendency is not dependent on manufacturing procedures such as annealing.

PET polymers provide a better barrier to gases when compared to polycarbonate and less tendency to allow odour elements through the bottle wall.  Polycarbonate has better scratch resistance and can be washed at temperatures between 60-70 degrees C without problems. You should obtain more return trips with polycarbonate compared with PET.  The cost of PET resin is less than polycarbonate, but the cost of equipment to make PET bottles is higher.  Polycarbonate can be recycled by grinding to make more bottles whereas PET does not retain the same degree of its original properties.

Other comparisons are possible, but hopefully this has provided you with some insight into the ongoing debate.